DE102014219970A1 - Piston, piston engine with such and motor vehicle with such a piston engine - Google Patents

Abstract

The invention relates to a piston (10) for a piston engine (1), comprising a piston head (11), a piston skirt (12) and a coating (20) arranged on a surface of the piston (10). According to the invention, it is provided that the coating (20) comprises an alloy based on iron-aluminum or an intermetallic compound based on iron-aluminum and is arranged so that it is at least partially in the assembled state of the piston (10) to a combustion chamber (40 ) of the piston machine (1) adjacent. Another aspect of the invention relates to a motor vehicle having a piston engine according to the invention.

Description

The invention relates to a piston for a piston engine, in particular a reciprocating engine. The invention further relates to a piston engine with such a piston and a vehicle having the piston engine.

Piston engines (also referred to as reciprocating piston engine) comprise a stationary component, namely a cylinder, and a piston arranged movably in the cylinder. The piston is essentially composed of a piston skirt, which is slidably mounted along the cylinder wall, and a piston crown. The piston crown, together with the cylinder, encloses a closed combustion chamber whose volume changes as a result of the movement of the piston in accordance with the working stroke of the engine. The respective position of the piston in the housing thus determines the size of the combustion chamber. A sealing of the combustion chamber relative to the crankcase takes place via sealing elements provided on the piston skirt of the piston. The materials used for such pistons are steels and aluminum-based light alloys.

The most widely used piston engines today are gasoline and diesel engines, which are used in particular in motor vehicles. In the case of motor vehicle engines, among other things, the piston has to transmit the gas forces acting in the combustion chamber to the connecting rod. In addition, he has the task of forwarding the heat of combustion transferred to him to the coolant.

The dissipation of thermal energy from the combustion chamber is necessary in order not to exceed the permissible component temperatures. On the other hand, however, the heat removal from the combustion chamber via the piston surface leads to unused efficiency potentials of internal combustion engines and lowers the exhaust gas temperatures. A further reduction in exhaust gas temperatures is caused by consumption-saving measures. In the case of modern diesel engines, the exhaust gas temperatures are already so low that the temperature of downstream catalysts after a cold engine start long time below the light-off temperature or the optimum operating temperature of the catalyst and therefore the optimal efficiency of exhaust aftertreatment is not achieved. In addition, the heat load on the piston crown can cause corrosion. Thus, measures are sought to increase the exhaust gas temperatures or at least not further reduce.

To counteract a heat dissipation from the combustion chamber, it makes sense to coat parts of the piston with insulating materials.

DE 196 03 515 C1 describes a spray material to improve the corrosion resistance of hot gas loaded components such as incinerators or gas turbines. For this purpose, a coating based on aluminum and iron is formed, which also contains traces of other metals, in particular chromium, silicon and carbon.

In DE 10 2006 007 148 A1 discloses a piston which is at least partially made of an iron-aluminum-chromium alloy in order to improve the mechanical properties of the piston, particularly with regard to the strength at higher temperatures.

Furthermore, ceramic piston inserts, ceramic overall pistons and steel pistons are used for thermal insulation. However, these products have been found to pose problems of stability, high cost and acoustics issues.

In EP 2 420 658 A1 a ceramic piston coating based on alumina is proposed. However, this has a low durability, especially when used in diesel engines.

WO 14030297 A1 discloses a silicone resin-based piston coating wherein heat-insulating hollow particles are embedded in the resin. The problem is that silicone resins for use in piston machines have too low a temperature resistance. The solution described therein also has the disadvantage that the hollow particles limit the maximum achievable insulation effect and thus further reduce the durability of the resin matrix.

The invention is based on the object to solve the problems of the prior art or at least reduce. In particular, a piston is to be provided with which an increase in the exhaust gas temperature and an improvement in efficiency can be achieved while maintaining high durability.

This object is achieved by a piston, a piston engine and a motor vehicle having the features of the independent claims.

Thus, the invention relates to a piston for a piston engine. The piston comprises a piston crown, a piston skirt and a piston surface on one surface of the piston, ie on the surface of piston crown and / or piston skirt, arranged coating. According to the invention, the coating comprises an alloy or an intermetallic compound based on iron-aluminum and is arranged such that, in the assembled state of the piston in the piston engine, it is adjacent, at least in sections, to a combustion chamber of the piston engine.

The arrangement of the coating according to the invention advantageously leads to an increase in the efficiency of the combustion process. The efficiency of the piston engine is particularly increased by the fact that less heat is removed from the combustion chamber or the cylinder chamber. In the combustion chamber thus prevail when using the piston according to the invention higher temperatures than known from the prior art. Higher temperatures in turn lead to a higher efficiency. In addition, a temperature increase in the combustion chamber has a positive effect on the exhaust gas treatment, since the exhaust gases also have a higher temperature and thus lead to an accelerated heating and catalyzing of the catalysts. Advantageously, the coating according to the invention on the piston ensures thermal insulation and / or corrosion protection of the piston surface or of the piston.

The coating according to the invention is particularly advantageous when used in diesel engines, since the relatively low diesel engine exhaust gas temperatures are increased by the coating according to the invention and thus the efficiency and the efficiency of the exhaust aftertreatment can be increased.

Piston machines are fluid-energy machines in which a displacer, namely the piston, defines by means of its movement a periodically varying working space. In the present invention, the reciprocating engine is understood as meaning both a rotary piston engine, which for example has a disk piston, and a reciprocating piston engine, in particular a cylindrical piston. The region of the piston, which faces the combustion chamber and thus is in contact with the air-fuel mixture or exhaust gas, is referred to in the present invention as a piston crown.

In reciprocating engines, which have pistons with a substantially cylindrical geometry, the piston crown in plan view has a round shape, which adjoins a cylindrical circumferential side wall, the piston skirt. The surface of the piston crown in turn can have a variety of contours. Thus, both planar and concave or convex curved shapes of the piston crown are possible in the present invention. Likewise, the piston head can have depressions and elevations, for example in the form of lugs, which are embedded in and / or protrude from the piston head.

Intermetallic compounds or intermetallic phases are homogeneous chemical compounds of two or more metals. In contrast to alloys, they show lattice structures that differ from those of the constituent metals. In their lattice, there is a mixed bond of a metallic bond fraction and lower atomic bonding or ion-binding fractions, which can result in superstructures. The presently preferred intermetallic compounds or alloys are each based on iron and aluminum. By this it is meant that at least 50% by weight of the intermetallic compound or alloy consists of iron and aluminum. The iron and aluminum based intermetallic compounds or alloys are also referred to herein as FeAl alloy or compound.

It is advantageous to coat the piston surface only in regions, in particular in the region of the piston crown, since this region communicates with the combustion chamber and thus with the highest temperatures. This embodiment thus brings a cost savings, without having to take losses in terms of the desired thermal insulation in purchasing. In addition, the surface material for the piston skirt in this embodiment can be optimized with regard to the desired mechanical and / or tribological properties.

In a preferred embodiment of the invention it is provided that the coating comprises 8 to 33 wt .-% aluminum. This is advantageous since aluminum, as the main constituent of the intermetallic compound or of the alloy, is property-determining in addition to iron in the preferred range.

The intermetallic compound or alloy which is preferred as the coating is distinguished in particular by the fact that, in addition to a particularly high temperature resistance of more than 500 ° C., it has a coefficient of thermal expansion which is compatible with the piston base material. This means that the volume expansion experienced by the coating as a result of temperature increase is so little different from the thermal expansion of the material of the piston crown and piston skirt that delamination does not occur. Thus, by a suitable choice of the composition of the compound, the life of the coating on the piston can be significantly increased.

A proportion of 8 to 33 wt .-% aluminum in the alloy (the FeAl-based alloy) or the FeAl intermetallic compound also leads advantageously to a coefficient of thermal expansion, which is very similar to that of conventional piston base materials, in particular of light metal piston. This applies in particular to pistons made of eutectic AlSi alloys as the base material, which have a thermal expansion coefficient of approximately α≈20 · 10e ^-6 K ^-1 . Particularly suitable here is the intermetallic compound Fe-24Al, ie a compound with a body-centered lattice structure (B2) and a mass fraction of 24% by weight of aluminum.

In a further preferred embodiment of the invention, the coating further comprises 0 to 10 wt .-% chromium (Cr), in particular 0.1 to 8 wt .-% Cr, preferably 1 to 7 wt .-% of Cr. It was found that the presence of chromium in the coating advantageously leads to better wet corrosion resistance. A coating, in particular in the form of an intermetallic compound, which has at least 16% by weight of aluminum and 5% by weight of chromium (Fe-16Al-5Cr) proved to be particularly advantageous with respect to wet corrosion resistance. Compositions having higher Al and / or Cr contents have still further improved wet corrosion resistance.

Furthermore, it is preferred that the coating has other elements in addition to iron, aluminum and chromium. Thus, in a further preferred embodiment of the invention, the coating 8 to 33 wt .-% Al, 0 to 10 wt .-% Cr, 0 to 10 wt .-% Co, 0 to 4 wt .-% Mo, 0 to 10 Wt% Ni, 0 to 5 wt% W, 0 to 5 wt% Re, 0 to 6 wt% Ta, 0 to 5 wt% Ti, 0 to 4 wt% V , 0 to 20 wt .-% Mn, 0 to 1 wt .-% Si, 0 to 10 wt .-% Nb, 0 to 2 wt .-% Hf, 0 to 1 wt .-% B, 0 to 5 wt % C, 0 to 0.3 wt% N, 0 to 3 wt% Zr, 0 to 3 wt% Y, 0 to 1 wt% Ce, 0 to 2 wt% Ga, 0 to 2 wt .-% La and 0 to 2 wt .-% Pt, wherein Fe and unavoidable impurities form the remaining 100 wt .-% remaining.

The advantage of these embodiments is that in particular the elements Co, Mo, Ni, W, Ti, V, Mn, Si, Nb increase the strength of the coating by solid solution formation with the connection matrix of Fe and Al and precipitation hardening. C and B, especially in conjunction with Ti, Hf and Zr, serve to precipitate formation of additional particles, which enhances the aforementioned effect. In addition, the addition of C to the coating has a positive influence on a machinability of the coating surface.

With particular advantage, the coating 10 to 30 wt .-% Al, 0 to 5 wt .-% Cr, 0 to 5 wt .-% Co, 0 to 4 wt .-% Mo, 0 to 5 wt .-% Ni , 0 to 4 wt .-% W, 0 to 3 wt .-% Re, 0 to 3 wt .-% Ta, 0 to 5 wt .-% Ti, 0 to 4 wt .-% V, 0 to 10 wt % Mn, 0 to 1 wt% Si, 0 to 5 wt% Nb, 0 to 2 wt% Hf, 0 to 1 wt% B, 0 to 2 wt% C, 0 to 0.3 wt .-% N, 0 to 3 wt .-% Zr, 0 to 1 wt .-% Y, 0 to 0.5 wt .-% Ce, 0 to 1 wt .-% Ga, 0 to 1 wt.% La and 0 to 1 wt.% Pt, Fe and unavoidable impurities forming the remainder to 100 wt.%.

Particularly preferred is that the coating 15 to 29 wt .-% Al, 0 to 5 wt .-% Cr, 0 to 4 wt .-% Mo, 0 to 2 wt .-% Ni, 0 to 4 wt .-% W, 0 to 5 wt .-% Ti, 0 to 4 wt .-% V, 0 to 1 wt .-% Si, 0 to 5 wt .-% Nb, 0 to 2 wt .-% Hf, 0 to 1 Wt .-% B, 0 to 2 wt .-% C, 0 to 0.3 wt .-% N, 0 to 3 wt .-% Zr, wherein Fe and unavoidable impurities to 100 wt .-% remaining Make rest.

The coatings composed in this way are distinguished by particularly low thermal conductivities of at most 14 W · m ^-1 K ^-1 , in particular of at most 13 W · m ^-1 K ^-1 , typically of approximately 12 W · m ^-1 K ^-1 . In addition, the thermal expansion coefficient of the coating is very similar to that of aluminum-based light metal compounds, so that a coating in one of these embodiments shows a very low delamination tendency.

In a further preferred embodiment of the invention it is provided that the piston crown and / or the piston skirt comprises or consists of a light metal alloy. Thus, the base piston is at least partially made of a light metal alloy. Under light alloy are basically all light metal alloys to understand that meet the mechanical requirements of a piston. Preferred in the present invention are aluminum alloys, especially aluminum-silicon alloys, where the silicon content is variable and can range up to hypereutectic concentrations. Particularly preferred are Al-Si12 base alloys which comprise 12% by weight of silicon (for example EN AC AlSi12CuNiMg).

These alloys have the advantage that they have a very similar to the coating according to the invention, in particular a coating with 10 to 30 wt .-% of aluminum, thermal expansion coefficients and thus reduce the Delaminationsneigung. This is minimized in particular if the difference in the coefficients of thermal expansion between the piston, in particular piston surface, and arranged thereon Coating maximum 10% based on a heating of 1 K is.

For the application of the coating to the piston head and / or the piston skirt, in a preferred embodiment, thermal spraying methods are preferred. These include in particular atmospheric plasma spraying, high-speed flame spraying, vacuum flame spraying and vacuum plasma spraying. Particularly good results with respect to the layer adhesion are achieved with high-speed flame spraying.

The invention further relates to a piston engine comprising at least one cylinder each having a piston arranged therein according to the present invention.

Furthermore, the invention relates to a motor vehicle having such a piston engine.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

The invention will be explained below in a preferred embodiment with reference to the accompanying drawings. It shows:

1 a schematic sectional view of a piston engine with a piston in a preferred embodiment of the invention.

A preferred embodiment of a piston engine with a piston according to the invention is based on a sectional view in the 1 shown a total with 1 indicated piston engine in the form of a reciprocating engine, preferably a diesel engine, represents. The piston engine 1 includes a cylindrical piston here 10 with a diameter d _K , which is in a cylinder 30 is arranged axially movable.

In the embodiment shown, the piston 10 a piston shirt 12 on, which is in the form of a cylinder jacket, as well as a substantially circular, planing piston crown 11 , piston crown 11 and piston shirt 12 are preferably formed in one piece and are preferably made of a light metal alloy. Particularly preferred are aluminum alloys, in particular aluminum-silicon alloys. The piston 10 also has circumferential grooves, which sealing elements 13 , so-called piston rings record.

The piston 10 is connected to a connecting rod, not shown, with a crankshaft for driving a vehicle. Also not shown are intake and exhaust ports and corresponding intake and exhaust valves and a fuel injector, which are arranged in the region of the cylinder head.

The piston 10 , in particular its piston crown 11 , and the cylinder 30 define a combustion chamber 40 , whose volume is determined by the position of the piston 10 is determined.

The piston bottom 11 has a coating according to the invention 20 with low thermal conductivity. When coating 20 it is preferably an intermetallic compound based on iron and aluminum, the other elements may be added. For example, the coating has 20 at a proportion of 10 to 30 wt .-% aluminum, a thermal conductivity of 12 W / mK on.

The coating 20 comes through their insulating properties to an insulating function. Due to the very low thermal conductivity λ of the coating 20 , only a small part of that is in the combustion chamber 40 resulting combustion heat over the surface of the piston crown 11 discharged from the cylinder space. Rather, the heat remains within the combustion chamber 40 and is thus available for the performance of mechanical work. This will be in the combustion chamber 40 realized a higher efficiency. Due to the high exhaust gas temperatures of the combustion chamber 40 discharged exhaust gas is also accelerated, the heating of a downstream catalyst system, whereby the catalytic exhaust gas treatment is optimized.

LIST OF REFERENCE NUMBERS

1

piston engine

10

piston

11

piston crown

12

skirt

13

sealing element

20

coating

30

cylinder

40

combustion chamber

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19603515 C1 [0006]
• DE 102006007148 A1 [0007]
• EP 2420658 A1 [0009]
• WO 14030297 A1 [0010]

Claims (10)

Piston ( 10 ) for a piston engine ( 1 ), comprising a piston head ( 11 ), a piston shirt ( 12 ) and one on a surface of the piston ( 10 ) arranged coating ( 20 ), characterized in that the coating ( 20 ) comprises an iron-aluminum-based alloy or an iron-aluminum-based intermetallic compound and is arranged to be in the assembled state of the piston ( 10 ) at least in sections to a combustion chamber ( 40 ) of the piston engine ( 1 ) adjoins. Piston ( 10 ) according to claim 1, characterized in that the coating ( 20 ) Comprises 8 to 33% by weight of aluminum. Piston ( 10 ) according to one of the preceding claims, characterized in that the coating ( 20 ) further comprises 0 to 10 wt% Cr. Piston ( 10 ) according to one of the preceding claims, characterized in that the coating ( 20 ) 8 to 33 wt .-% Al, 0 to 10 wt .-% Cr, 0 to 10 wt .-% Co, 0 to 4 wt .-% Mo, 0 to 10 wt .-% Ni, 0 to 5 wt % W, 0 to 5 wt% Re, 0 to 6 wt% Ta, 0 to 5 wt% Ti, 0 to 4 wt% V, 0 to 20 wt% Mn, 0 to 1 wt% Si, 0 to 10 wt% Nb, 0 to 2 wt% Hf, 0 to 1 wt% B, 0 to 5 wt% C, 0 to 0.3 Wt .-% N, 0 to 3 wt .-% Zr, 0 to 3 wt .-% Y, 0 to 1 wt .-% Ce, 0 to 2 wt .-% Ga, 0 to 2 wt .-% La and 0 to 2 wt.% Pt, and Fe and unavoidable impurities form the balance remaining at 100 wt.%. Piston ( 10 ) according to one of claims 1 to 3, characterized in that the coating ( 20 ) 10 to 30 wt .-% Al, 0 to 5 wt .-% Cr, 0 to 5 wt .-% Co, 0 to 4 wt .-% Mo, 0 to 5 wt .-% Ni, 0 to 4 wt % W, 0 to 3% by weight of Re, 0 to 3% by weight of Ta, 0 to 5% by weight of Ti, 0 to 4% by weight of V, 0 to 10% by weight of Mn, 0 to 1 wt% Si, 0 to 5 wt% Nb, 0 to 2 wt% Hf, 0 to 1 wt% B, 0 to 2 wt% C, 0 to 0.3 Wt% N, 0 to 3 wt% Zr, 0 to 1 wt% Y, 0 to 0.5 wt% Ce, 0 to 1 wt% Ga, 0 to 1 wt% % La and 0 to 1 wt% Pt, and Fe and unavoidable impurities form the balance remaining at 100 wt%. Piston ( 10 ) according to one of claims 1 to 3, characterized in that the coating ( 20 ) 15 to 29 wt .-% Al, 0 to 5 wt .-% Cr, 0 to 4 wt .-% Mo, 0 to 2 wt .-% Ni, 0 to 4 wt .-% W, 0 to 5 wt % Ti, 0 to 4 wt% V, 0 to 1 wt% Si, 0 to 5 wt% Nb, 0 to 2 wt% Hf, 0 to 1 wt% B, 0 to 2 wt .-% C, 0 to 0.3 wt .-% N and 0 to 3 wt .-% Zr, and Fe and unavoidable impurities form the remaining 100 wt .-% balance. Piston ( 10 ) according to one of the preceding claims, characterized in that the piston crown ( 11 ) and / or the piston skirt ( 12 ) comprise or consist of a light metal alloy, in particular an aluminum-silicon alloy. Piston ( 10 ) according to one of the preceding claims, characterized in that the coating ( 20 ) and the piston crown ( 11 ) have a different by a maximum of 10% thermal expansion coefficient. Piston machine ( 1 ), comprising a cylinder ( 30 ) and a piston arranged therein ( 10 ) according to one of claims 1 to 8. Motor vehicle having a piston engine ( 1 ) according to claim 9.

Images